Bone stabilization device

ABSTRACT

A device and method for stabilizing a broken bone while it heals is disclosed. The device preferably has a (a) first (or proximal) section with a driving head, threads and a first diameter, and (b) second (or distal) section that is threaded and has a second diameter. The first section is preferably greater in diameter than the second section so that greater torque can be applied to tighten the device. The device may include one or more self-tapping structures to lessen the torque required to screw it into a bone.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

The present application is a continuation of U.S. patent applicationSer. No. 14/993,972, filed Jan. 12, 2016, entitled “BONE STABILIZATIONDEVICE,” the entirety of which is hereby incorporated by referenceherein.

FIELD OF THE INVENTION

The present invention relates to a device implantable in a bone tostabilize it while it heals, and which is particularly suitable for usein a metacarpal bone.

FIELD OF THE INVENTION

The palm of the hand is made up of bones called metacarpals, and ametacarpal connects each finger and thumb to the hand. Each finger andthumb is formed of bones called phalanges. The connection of thephalanges to the metacarpals is called a “knuckle” joint ormetacarpophalangeal joint (MCP joint), and acts like a hinge when thefingers or thumb are bent. In the metacarpal bones, the proximal portionand mid metacarpal portion is relatively narrower, and the distalportion is relatively wider with respect to both the internal medullarycanal and external diameter.

In each finger, there are three phalanges that are separated by twojoints called the interphalangeal joints (IP joints). The proximal IPjoint (PIP joint) is the one closest to the MCP joint. The other jointclosest to the end of the finger is the distal IP joint (DIP joint). Thethumb just has one IP joint. The joints are covered on the ends witharticular cartilage.

Damage to the metacarpal bone may occur as a result of a sprain orfracture. Typically, once the metacarpal bone is lined up after aninjury it must be stabilized in position while it heals.

To stabilize a broken metacarpal bone, it is now known to use anon-threaded, smooth metal shaft (hereafter “nail”) positioned in themetacarpal bone to hold it in position while the bone heals. An openingis first formed in the metacarpal bone, wherein the opening extendsthrough the fracture and the nail is positioned in the opening toprovide lateral stability for the parts of the bone on either side ofthe fracture. After a certain period, a second surgery is required toremove the nail from the bone. Problems with the nail are that, becauseit is not anchored in the bone, it can migrate through the metacarpalbone and into surrounding tissue. Sometimes this can result in damage tosoft tissue, such as a severed or damaged tendon or cartilage, and/orcause pain. Another problem with the nail is that, because it canmigrate, a second surgery is required to remove it. Additionally, theproximal end of pins and nails can cause tendon irritation, tendonrupture or skin irritation and infection.

One potential solution to this problem is to insert a screw into thebone. Such a procedure could be lengthy, and there would be apossibility of bone damage, or damage to the driving head of the screw,which could prevent complete insertion of the screw into the bone, orbreakage of the screw because the screw must be relatively long andslender. Current screws are not designed specifically for intramedullaryplacement. They are not long enough, and if a current screw design wassimply lengthened, it would lack a shaft and driving portion sufficientto handle the torque required.

SUMMARY OF THE INVENTION

The present invention solves the problems associated with repairing abone, such as a metacarpal bone, by providing a device that is a screwhaving a first (or proximal in relation to the screw) section and asecond (or distal in relation to the screw) section. As used herein withrespect to a device, or section of a device, according to the invention,“diameter” includes the diameter of the threads, unless otherwisespecified. The first section preferably has a greater diameter than thesecond section, and the end (or tip) of the first section has a drivingsurface (or hand) to receive and be turned by an appropriate drivingtool. The screw is inserted into the metacarpal in a retrograde fashion.In this manner, the smaller diameter second section can fit in thenarrower proximal and mid portion of a bone, such as a metacarpal bone.The larger diameter first section fits into the larger, distal portionof the bone (such as a metacarpal head), and the driving head at the endof the first section is wider in order to accept a larger driving tooland generate more torque to drive the screw into position.

In preferred embodiments, the device has a cutting structure at the tipof the second end, and a second cutting structure between the firstsection and second section. The cutting structures (either one, two ormore, if used) assist in placing the screw into the bone with lesstorque.

It is also preferred, but not required, that there is an immediate stepfrom the thicker diameter of the first section to the thinner diameterof the second section, and that the second cutting structure bepositioned immediately before, or be included as part of, the initialthreads in the first section, and that the cutting structure beapproximately the same diameter as the first section.

In one exemplary embodiment, the second section is completely threaded(which as used herein means substantially completely threaded) and hasan overall outer diameter (including the threads) of 4 mm. The firstsection is also preferably completely threaded (which as used hereinmeans substantially completely threaded) and has an overall outerdiameter of 4.5 mm. The first section, however, may have a diameter of3.0 mm-5.0 mm, and the second section may have a diameter of 3.0 mm-4.5mm. It is preferred that the diameter of the first section be about 0.5mm greater than the diameter of the second section. The first sectionmay instead have a diameter that is 7%-15% greater than the diameter ofthe second section.

The threads most preferably run along the entire length (which meanssubstantially the entire length) of the device. The threads may have thesame pitch and height along the length of the device, or the threads onthe first section may have a different pitch and/or height than thethreads on the second section.

Because of the configuration of device according to the invention, thedevice may be inserted and retained in a bone such as the metacarpal.The device generates sufficient fixation to the bone, is thin enough tofit into the proximal and middle portions of the bone, and strong enoughso that torque applied to it threads the device into the bone ratherthan causing the device to deform.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of the head of one embodiment of a device accordingto the invention.

FIG. 2 is a cross-sectional side view of the device of FIG. 1.

FIG. 3 is a perspective, side view of the device of FIGS. 1 and 2.

FIG. 4 is a partial, cross-sectional side view of the device of FIGS.1-3.

FIG. 5 is an end view of the device of FIGS. 1-4.

FIG. 6 is a partial, cross-sectional side view of the device of FIGS.1-5.

FIGS. 7-7B show one method for installing a device according to FIGS.1-6 into a metacarpal bone.

FIGS. 7C and 8 illustrate the device of FIGS. 1-6 positioned in ametacarpal bone.

FIG. 9 illustrates a side view of the device of FIGS. 1-6 with a cuttingflute shown without threads for clarity.

FIG. 10 illustrates a detailed view of a portion of the device of FIG. 9with a distal cutting flute shown without threads for clarity.

FIG. 11 illustrates a detailed view of a portion of the device of FIG. 9with a proximal cutting flute shown without threads for clarity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Turning now to the figures, where the purpose is to describe preferredembodiments of the invention and not to limit same, FIG. 1 shows anexemplary embodiment 10 of the invention. Device 10 may be formed of anysuitable material, such as titanium steel, stainless steel or nitinol.Device 10 has a first (or proximal) section 12, a second (or distal)section 14, and a shaft 16 with an outer surface 17. Device 10 may bebetween 3.5 cm and 8.5 cm or between 6.5 cm and 8 cm in length, or havea length of about 7 cm.

First section 12 has first threads 10A which preferably have a height ofabout 0.5 to 1 mm as measured from outer surface 17, and a pitch ofabout 1 mm per revolution. A driving surface, or head 18 is shown asbeing the same diameter of first section 12, but head 18 may have adifferent diameter or be of a different shape, such as triangular. Head18 may accept any suitable driver configuration, such as a Torx drive,slotted, Pozidriv, Robertson, tri-wing, Torq-Set, SpannerHead, TripleSquare, and hex head. A cutting structure 20 is shown in FIGS. 3, 9, and11 as positioned at the distal end of first section 12, and itpreferably has the same height as threads 10A, or is formed in one ormore threads 10A, and the portion of section 12 that includes cuttingstructure 20 as shown preferably has the same diameter as the rest offirst section 12. The preferred configuration of cutting structure 20 isself-tapping features in one or more threads 10A, which are preferablyindentations that basically make the thread serrated, as shown in FIG.3. First section 12 preferably has a diameter of 3.0 mm to 5.0 mm, andmost preferably about 4.5 mm. First section 12 preferably extendsbetween about 25% to 45% of the length of device 10, and in onepreferred embodiment is about 40% of the length.

Second section 14 has first threads 14A which preferably have a heightof about 0.5-1 mm as measured from outer surface 17, and a pitch ofabout 1 mm/revolution. A cutting structure 28 is shown in FIGS. 3, 9,and 10 at the distal tip 30 of second section 12, which may be any knownself-tapping feature. Second section 14 preferably has a diameter of 3.0mm to 4.5 mm, most preferably about 4.0 mm, and most preferably about0.5 mm less than the diameter of the first section. Second section 14preferably extends between about 55% to 75% of the length of device 10,and in one preferred embodiment is about 60% of the length.

Threads 10A on the first section 10 preferably have the same pitch asthe thread 14A, and extend outward from surface 17 of device 10 by thesame amount as threads 14A, although any suitable thread configurationis acceptable, including threads with differential pitches threads oneither or both of sections 12 and 14.

Device 10 may be cannulated or non-cannulated. As shown, device 10 has acannula 32 extending therethrough. A non-cannulated device may be have asmaller diameter than a cannulated device.

The diameter of the first section is preferably about 4%, or 5%, or 4%to 7%, or 4% to 10%, of the length of device 10.

FIGS. 7-7B depict a method for installing device 10 into a fracturedmetacarpal bone. In FIG. 7, the fracture in the bone is first aligned,and then a K-wire is inserted into the bone. A K-wire or pin is known inthe art and is a sterilized, smooth steel pin used in orthopedics andother types of medical applications. It is available in different sizesas needed and provides structure, support and in one version has adiameter of about 0.040″.

In FIG. 7A a cannulated drill, using the K-wire as a guide, drills anopening into the metacarpal bone, wherein the opening extends throughthe fracture, or partially through the k wired construct, and providesenough space on each side of the fracture to properly position device10.

In FIG. 7B, device 10 is rotatingly driven into the opening in themetacarpal bone using cannulated techniques. Second section 14 is firstdriven in, and then first section 12 is driven in. The width of secondsection 14 and first section 12 are both greater than the opening formedin the bone, so each section can thread into the opening. This providesbone material for the threads to grasp and retain device 10 in theopening.

FIGS. 7C and 8 show device 10 in the metacarpal bone after the K-wirehas been removed. Since device 10 is anchored in the metacarpal bone,there is no need for a second operation to remove it.

If a non-cannulated device is used, the K wire may be used to form apilot hole, and device 10 would be driven into the pilot hole.

In another aspect of the invention, the device has a single diameterwith threads of the same pitch and height. This device may have a headsimilar to the one described above, but that is about 0.5 mm wider thanthe rest of the device, or about 7%-15% wider, in order to generatesufficient torque. Such a device may also have multiple self-tapping, orcutting structures, in order to reduce the amount of torque required toscrew the device into an opening in a bone. For example, such a devicemay have one cutting structure at its distal tip, and one or more othercutting structures along its length, and/or a cutting structurejuxtaposed the head so the head of the device does not extend beyond thebone.

Specific exemplary embodiments of the invention are described below:

1. A device for repairing a bone, the device for being received in thebone and comprising:

-   -   (a) a shaft having a length and an outer surface;    -   (b) a first end and a second end;    -   (c) threads on the outer surface, wherein the threads comprise        85% or more of the shaft length; and    -   (d) a driving surface at the first end,        -   wherein the first section has a larger diameter than the            second section of the device.            2. The device of example 1 wherein the device is comprised            of one or more of nitinol, stainless steel and titanium            steel.            3. The device of example 1 or 2, wherein the first section            has a self -tapping configuration and the second section has            a self-tapping portion.            4. The device of any of examples 1-3 wherein the first end            has a diameter at least 7% wider than the diameter of the            second end.            5. The device of any of examples 1-4 wherein the first end            has a diameter that is 7%-15% wider than the diameter of the            second end.            6. The device of any of examples 1-5 that has that has a            length of between 3.5 cm and 8.5 cm, or 3.5 to 7.5 cm, or            4.0 to 8.0 cm, or about 7 cm.            7. The device of any of examples 1-6 wherein the first            diameter is between 3.5 mm and 5.0 mm.            8. The device of any of examples 1-7 wherein the second            diameter is between 3.0 mm and 4.5 mm.            9. The device of any of examples 1-8 that further includes a            cutting surface at the second end.            10. The device of any of examples 1-9 that further includes            a cutting surface between the first end and the second end.            11. The device of any of examples 1-10 that includes a            cannula.            12. The device of any of examples 1-11 wherein the first end            is between 0.3 mm and 0.7 mm greater in diameter than the            diameter of the second end.            13. The device of any of examples 1-12 wherein the first end            is between 7% and 15% greater in diameter than the diameter            of the second end.            14. The device of any of examples 1-13 wherein the threads            on the first end have the same pitch as a pitch of the            threads on the second end.            15. The device of any of examples 1-13 wherein the threads            on the first end have a different pitch than a pitch of the            threads on the second end.            16. The device of any of examples 1-15 wherein the threads            are continuous along the length of the device.            17. The device of any of examples 1-16 wherein the threads            on the first section comprise up to 40% of the length of the            device.            18. The device of any of examples 1-17 wherein the driving            head is selected from the group consisting of designs that            can accept one of the following drivers: a flat screwdriver,            a Phillips screw driver, a hex head, and an Allen wrench.            19. The device of any of examples 1-8 wherein the driving            head has the same diameter as the first end.            20. The device of any of examples 1-19 wherein the threads            have the same height.            21. The device of any of examples 1-20 wherein the threads            have the same height and pitch.            22. The device of any of examples 1-21 that has a length and            the diameter of the first section is at least 4%, or at            least 5%, of the length.            23. The device of any of examples 1-21 that has a length and            the diameter of the first section is between 4% and 7% of            the length.            24. The device of any of examples 1-21 that has a length and            the diameter of the first section is between 4% and 10% of            the length.

Having thus described some embodiments of the invention, othervariations and embodiments that do not depart from the spirit of theinvention will become apparent to those skilled in the art. The scope ofthe present invention is thus not limited to any particular embodiment,but is instead set forth in the appended claims and the legalequivalents thereof. Unless expressly stated in the written descriptionor claims, the steps of any method recited in the claims may beperformed in any order capable of yielding the desired result.

1. (canceled) 2.-23. (canceled)
 24. A method of implanting a cannulatedintramedullary implant within an intramedullary canal of a metacarpalfor fixation of a fracture, the method comprising: inserting a guidewireinto the intramedullary canal of the metacarpal; drilling an openinginto the metacarpal past a location of the fracture guided by theguidewire; rotatably driving the cannulated intramedullary implant intothe intramedullary canal guided by the guidewire, the implant comprisinga headless shaft having a trailing end and a leading end, the shaftcomprising a thread of a constant pitch along an entire length of theshaft, wherein a first portion of the thread has a greater constantmajor diameter and a second portion of the thread has a smaller constantmajor diameter, the first portion of the thread being continuous withthe second portion of the thread, and wherein the first portion of thethread engages bone material in a larger distal portion of themetacarpal and the second portion of the thread engages bone material ina narrower proximal and mid portion of the metacarpal such that thecannulated intramedullary implant is anchored in the metacarpal; andremoving the guidewire.
 25. The method of claim 24, wherein thecannulated intramedullary implant is inserted with the leading endentering the opening into the intramedullary canal first, the secondportion of the thread being closer to the leading end than to thetrailing end.
 26. The method of claim 24, wherein the first portion ofthe thread engages the metacarpal head.
 27. The method of claim 24,wherein a first root diameter of the shaft at the first portion of thethread is greater than a second root diameter of the shaft at the secondportion of the thread.
 28. The method of claim 27, wherein the firstportion and the second portion of the thread is of the same threadheight.
 29. The method of claim 27, wherein the shaft further comprisesa transition region, a root diameter of the transition regiontransitions from the first root diameter to the second root diameter.30. The method of claim 24, wherein the shaft comprises a driving headat the trailing end, the driving head configured to receive a driverthat applies a torque to rotatably drive the cannulated intramedullaryimplant into the intramedullary canal.
 31. The method of claim 24,wherein the shaft comprises at least one cutting structure extendingthrough part of the first portion of the thread and at least anothercutting structure extending through part of the second portion of thethread.
 32. A intramedullary implant configured to be implanted withinan intramedullary canal of a metacarpal for fixation of a fracture: aheadless shaft having a trailing end and a leading end, wherein theshaft comprises: a driving recess at the trailing end and configured toreceive a driver; a first portion closer to the trailing end, the firstportion comprising a first thread and a first root diameter which tapersto a smaller second root diameter; and a second portion closer to theleading end, the second portion comprising a second thread and thesmaller second root diameter, wherein the first thread and the secondthread have the same pitch, the first and second threads each comprisinga cutting flute extending through a portion of the first and secondthreads respectively, and wherein the shaft is cannulated throughout alength of the shaft.
 33. The implant of claim 32, wherein the drivingrecess is shaped to receive a flat screwdriver, a Phillips screwdriver,a hex head, or an Allen wrench.
 34. The implant of claim 32, wherein thefirst portion has a major diameter so that the first thread isconfigured to engage a larger distal portion of the metacarpal.
 35. Theimplant of claim 34, wherein the second portion has a major diameter sothat the second thread is configured to engage a narrower proximal ormid portion of the metacarpal.
 36. The implant of claim 32, wherein theshaft has a wall thickness so that the implant is strong enough to berotatably driven into bone material of the metacarpal by a torquewithout being deformed.
 37. A method of implanting a cannulatedintramedullary implant within an intramedullary canal of a metacarpalfor fixation of a fracture, the method comprising: inserting a guidewireinto the intramedullary canal of the metacarpal; drilling an openinginto the metacarpal past a location of the fracture guided by theguidewire; rotatably driving the cannulated intramedullary implant intothe intramedullary canal guided by the guidewire, the implant comprisinga headless shaft having a trailing end and a leading end, the shaftcomprising a thread of a constant pitch, wherein a first portion of theshaft closer to the trailing end has a greater outer diameter and asecond portion of the shaft closer to the leading end has a smallerouter diameter, and wherein threads on the first portion engage bonematerial in a larger distal portion of the metacarpal and threads on thesecond portion engage bone material in a narrower proximal or midportion of the metacarpal such that the cannulated intramedullaryimplant is anchored in the metacarpal; and removing the guidewire. 38.The method of claim 37, wherein the cannulated intramedullary implant isinserted with the leading end entering the opening on the intramedullarycanal first.
 39. The method of claim 37, wherein the threads on thefirst portion engages the metacarpal head.
 40. The method of claim 37,wherein the shaft has a wall thickness so that the implant is strongenough to be rotatably driven into the metacarpal by a torque withoutbeing deformed.
 41. The method of claim 37, wherein the threads on thefirst portion and the threads on the second portion are of the samethread height.
 42. The method of claim 37, wherein rotatably driving thecannulated intramedullary implant is performed using a driving head, theimplant comprising a driving head at the trailing end configured toreceive the driving head.
 43. The method of claim 42, wherein thedriving head is a flat screwdriver, a Phillips screwdriver, a hex head,or an Allen wrench.